Technical Field
The present disclosure relates to a fuel cell stack.
Background Art
As one of the environmentally friendly power sources, a fuel cell is often used. For example, a polymer electrolyte fuel cell mainly includes a membrane electrode assembly (MEA) that includes an electrolyte membrane with catalyst layers sandwiching opposite surfaces thereof, gas diffusion layers provided on opposite outer sides of the catalyst layers, and a pair of separators sandwiching the entire boy from the right and left sides thereof. A plurality of such cells are stacked while being electrically connected in series, so that the fuel cell stack is formed.
When a fuel cell generates power, the cell is exposed to a corrosive environment. Therefore, SUS with excellent corrosion resistance is typically used as the base material of each separator of the cell. However, when the potential of the cell becomes high (greater than or equal to about 1 V) in the corrosive environment, the metal would unavoidably dissolve. This is because cooling water for the fuel cells flows through the fuel cell stack such that the water contacts every cell. Therefore, an equivalent circuit is formed as described below. In addition, since the cells in the fuel cell stack are arranged in series, the voltage becomes high and a large corrosion current flows through a plurality of cells located at the positive-side end of the fuel cell stack, and thus the potential therein becomes high. Consequently, corrosion (dissolution) occurs in the base materials of the separators (For example, SUS). It should be noted that in the present disclosure, “corrosion” or “dissolution” means a state in which a metallic material is ionized and thus dissolves so that the plate thickness decreases.
Measures for preventing such corrosion (dissolution) of the base materials of the separators have been proposed. For example, JP 2005-293876 A describes a fuel cell stack formed by stacking a plurality of unit cells each having metal separators of the same type, obtained by applying surface treatment to the metal separators of one or more cells located at the positive-side end of the fuel cell stack by which the corrosion resistance of the metal separators becomes relatively higher than those of the metal separators used for the other cells. As the surface treatment for providing high corrosion resistance, a plating process that uses noble metal, such as gold or silver, or a plating process that forms thick plating are exemplarily illustrated, and as the surface treatment for providing low corrosion resistance, a plating process that forms thinner plating is exemplarily illustrated.
JP 2005-293874 A describes a fuel cell stack with a configuration in which a pair of terminal plates are arranged at opposite ends of a cell stack having a plurality of stacked unit cells, in which fluid channels for supplying or discharging reactant gas and cooling water to/from the cell stack are allowed to communicate with only an inlet port and an outlet port that penetrate the negative-side terminal plate. That is, since oxidation current flows through the positive-side terminal plate, the cell stack is configured such that the cooling water or moisture of reactant gas flowing through the fluid channels does not contact the positive-side end plate, whereby an improvement in the corrosion resistance of the positive-side terminal plate and cost reduction are achieved. JP 2005-293874 A also discloses arranging a cutoff plate for cutting off moisture permeation between the positive-side terminal plate and the cell stack.
In addition, JP 2015-69737 A describes a configuration of a fuel cell stack including power-generating cells and a non-power-generating dummy cell(s), in which the dummy cell is arranged at one or each end of the plurality of stacked power-generating cells. Using a dummy cell can suppress flatting at one or each end of the cells in the stacked direction and a voltage drop due to contamination.